docs: admin-guide: hw-vuln: avoid using ReST :doc:`foo` markup

The :doc:`foo` tag is auto-generated via automarkup.py.
So, use the filename at the sources, instead of :doc:`foo`.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/4e378517761f3df07165d5ecdac5a0a81577e68f.1623824363.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst

@@ -3,7 +3,8 @@
 SRBDS - Special Register Buffer Data Sampling
 =============================================
 
-SRBDS is a hardware vulnerability that allows MDS :doc:`mds` techniques to
+SRBDS is a hardware vulnerability that allows MDS
+Documentation/admin-guide/hw-vuln/mds.rst techniques to
 infer values returned from special register accesses.  Special register
 accesses are accesses to off core registers.  According to Intel's evaluation,
 the special register reads that have a security expectation of privacy are